As an example, the conversational search task in the TREC Conversational Assistant Track (CAsT) [1]}, [2]} is defines as follows.
Given a series of natural conversational turns for a topic \(\mathcal {T}\)  with queries for each turn \(\mathcal {T}=\lbrace Q_1,...Q_i...,Q_n\rbrace \) , the task is to identify a set of relevance documents (or passages) \(\mathcal {D}_i\)  for each turn \(Q_i\)  to satisfy the information needs in turn \(i\)  with the context in turn \(Q_{<i}=Q_1 : Q_{i-1}\) .
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